The tethered-float breakwater is a unique concept constructed of numerous 

 buoyant floats with a characteristic dimension about equal to the wave height. 

 The floats are independently tethered at or below the water surface in a water 

 depth many times the float diameter. They are driven in opposition to the 

 waves by the pressure gradient, and the dominant attenuation mechanism is drag 

 resulting from the buoy motion. Because of their dynamic response, there is a 

 possibility that the buoys will pendulate in the incoming wave field out of 

 phase with the orbital motions. This out-of-phase motion transforms wave 

 energy into turbulence and ultimately into heat. 



The five concepts (pontoons, sloping float, scrap tire, cylinders, and 

 tethered float) discussed appear to be the dominant floating breakwater types 

 which merit serious evaluation and investigation where conditions are suit- 

 able. Other floating structures have been developed as wave attenuators, but 

 for the most part appear to be complex arrangements with various degrees of 

 complicated construction features. These five concepts have shown much 

 promise for wide application but are in need of additional laboratory and 

 field evaluation from a three-dimensional standpoint of wave transmission and 

 mooring loads. The response of floating breakwaters to certain critical, 

 irregular wave conditions and to oblique waves requires further investiga- 

 tion. Evidence indicates that long-crested waves do not strike an entire 

 section of floating breakwater simultaneously (except for unusual occurrences 

 such as boat wave generation); hence, the usual two-dimensional wave tank 

 investigations probably provide highly conservative mooring data. 



Theoretical work by Richey and Adee (1975) tends to indicate that the 

 water volume (mass) displaced by a given breakwater section is more important 

 for performance than the shape of the cross section. This conclusion has 

 ramifications regarding materials to be used in the breakwater construction; 

 e.g., no advantage is gained by using lightweight concrete. Mixing and 

 placing standards are easier to maintain with standard concrete which has a 

 long history of successful performance in both saltwater and freshwater. 

 Sutko and Haden (1974) believe that a square cross section gives slightly 

 better wave reduction than a triangular, circular, or trapezoidal section. 

 The ballast should be concentrated low in the profile, and performance seems 

 to be best when submergence is about two-thirds of the structure height. 

 Stormer (1979) feels the designs should be kept as simple, durable, and 

 maintenance-free as possible to avoid highly complex structures that are 

 difficult and expensive to design, construct, and maintain. The weak links in 

 a floating breakwater are quality control during construction of the break- 

 water units and the connections used to attach various modules of the system. 



3. Construction Materials and Structure Features. 



The reinforced concrete pontoon-type structures with a foam core for flo- 

 tation currently appear to be the most widely accepted floating breakwaters 

 meeting the standard wave climate. The use of scrap tires for construction 

 material may be an exception; however, Steiner (no date) states that extensive 

 experience with European floating breakwaters indicates the concrete floating 

 pontoon breakwater should always be given prominent consideration. 



Two important parameters for floating breakwater design include (a) the 

 ratio of structure width-to-wavelength, and (b) the ratio of water depth-to- 

 wavelength. A typical design of concrete pontoon floating structure uses a 



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